The selection of any filtration equipment for the purpose of providing continuous cleaning for circulating liquid is the result of many considerations. Obviously, the filtration system must accomplish removal of undesirable elements from a liquid flow stream even though the undesirable elements may vary widely with regard to the particular type of filtration system that might be designed for separation of the same from a carrier fluid. For example, the removal of bacteria or other micro-organisms may require the use of sophisticated sanitary filters while the removal of unwanted odors or liquid turbidity may call for the use of depth filtration, through layers of sand, charcoal or diatomaceous earth, in which the passages grow increasingly more restrictive. Many filter applications, however, are concerned only with the separation of specific solids from a liquid stream. This kind of application is frequently accomplished with surface-type filters utilizing fibrous cartridges or mesh screens composed of either woven wire or fabric material. This category includes filters having the primary capability of removing solid particulate from oil and gas well completion fluids as well as circulating fluids employed in other commercial activities. While the present invention is discussed herein particularly with regard to the relation thereof to wells that are capable of producing petroleum products, it is not intended to limit the invention to the clening of liquids that are ordinarily employed for completion and workover activities in conjunction with deep wells of this nature. It is intended within the scope of the present invention to provide a liquid cleaning system that may be effectively employed in conjunction with a wide range of commercial activities. For purposes of simplicity, however, the invention is described herein particularly as it relates to the cleaning of liquid that is employed during completion and workover activites in connection with deep wells capable of producing petroleum products.
As is the case with most types of equipment, the choice of filtration equipment is a process of evaluating alternatives. Overall costs must be weighted, and the effect of the filtration system on the particular production involved must also be given careful consideration. In the case of filtration systems, it is important to consider whether the filtration medium can be maintained or regenerated in order to provide for continuous or substantially continuous commercial liquid circulation activities without shutting down the commercial system in order for the filtration system to be restored to the commercially effective quality thereof.
With regard to liquid filtration systems, the liquid filters fall into three general categories including replaceable filters, filters that may be manually or mechanically cleaned and filters that may be restored to operative quality by means of backwashing. With regard to replaceable filters, no effort is typically made to clean or regenerate the filtering media. Instead, the filter is typically in the form of a cartridge that may be removed from the liquid circulation system and disposed of and with regeneration of the filter system taking the form of clean cartridges being inserted in the place of the cartridges that are removed for disposal. Typical examples of this media include disposable cartridge filters, bag filters, pad filters and the like. Among these, the cartridge filter is probably the most commonly used. These filters may offer a lower installed cost, and are generally utilized in low flow applications with relatively clean liquids. However, the frequency of replacement can present a prohibitive operating cost to utilization of cartridge filters. Other disadvantages may include excessive labor costs, down time of the liquid processing system, bypassing of fluid around the cartridge due to seal failure, and transportation, storage and disposal of spent filter cartridges. The most significant of these disadvantages is down time of the commercial activity that requires circulation of the liquid that is contaminated and is required to be cleaned during continuous circulation. In the case of oil and gas wells in particular, shutting down the liquid circulation process during completion and workover activities can result in extremely expensive costs, especially in the case of offshore wells which require extremely expensive personnel and equipment for conducting such activities.
In the case of manual or mechanical cleaning of filters, most filters that are employed are of relatively expensive construction and require high labor costs in order to achieve removal and restoration of the filters and for accomplishing removal of the solid particulate from the filters themselves. Mechanical cleaning of filters often results in high maintenance costs due to the necessary close tolerance of moving parts that are required.
Backwashing systems for removal of accumulated solid particulate from liquid filters involve a reversal of liquid flow through the medium. This process is common to sand and in-line pressure filters. Backwashing sand filters require large volumes of liquid at low flow rates to prevent the breakup of the sand bed, which must be replaced periodically.
Tubular pressure filters are backwashed quickly and in place with a minimum loss of liquid. Where tubular pressure filters are utilized for separating solid paticulate from a circulating fluid medium, it is typical for the fluid circulation system to be shut down periodically in order to allow the filters to be backwashed. It is desirable to provide a backwashing system that enables the liquid circulation system to be maintained in continuous operation and yet allows the tubular filter to be cleaned as often as is appropriate to obtaining optimum filtering characteristics.
During typical filter backwashing operations, a volume of liquid matter is typically lost since the liquid material itself it utilized to transport the accumulated solid particulate to a suitable receptable for disposal. In many cases, especially in conjunction with completion and workover operations in oilwells, the liquid medium, which is typically a brine, is of quite expensive nature. It is desirable, therefore, to provide a liquid backflushing system for accomplishing removal of accumulated particulate from tube or cartridge type filters and further to provide means for recovery of substantially all of the liquid that is employed in the backflushing operation for subsequent reuse.
In view of the foregoing, it is a primary feature of the present invention to provide a novel liquid filtration system allowing continuously circulating fluid to be continuously cleaned of solid particulate and enabling the filters of the filtration system to be restored by backflushing operations without requiring the liquid circulation system to be shut down.
It is another feature of the present invention to provide a novel liquid filtration system whereby liquid utilized for filter backflushing operations is recovered and is fed back into the liquid cleaning system, thereby minimizing any loss of fluid during the fluid cleaning operation.
It is another feature of this invention to provide another novel liquid filtration system for continuously circulating liquid whereby the contaminated liquid is subjected to preliminary mechanical separation to remove large particulate and debris from the contaminated liquid and is then subjected to filtration by means of a filter bank in order to remove all solid particulate above a predetermined size from the contaminated liquid.
It is an even further feature of this invention to provide a novel fluid filtration system for continuously circulating liquid, wherein liquid utilized for backflushing the filter system and transporting accumulated solid particulate therefrom is subjected to centrifugal separation for removal of a majority of the solid particulate from the backflushing liquid and wherein the cleaned backflushing liquid is then recirculated through the filtration system for recleaning and subsequent use.
Other and further objects, advantages and features of the present invention will become apparent to one skilled in the art upon consideration of this entire diclosure. The form of the invention, which will now be described in detail, illustrates the general principles of the invention, but it is to be understood that this detailed description is not to be taken as limiting the scope of the present invention. For example, although the present invention is described principally as it relates to utilization in conjunction with circulation system for completion and workover of deep wells for producing petroleum products, it is intended that the invention be applicable to other continuous liquid circulation systems as well.